Mal de Rio Cuarto Virus (MRCV) is considered to be the most prevalent and destructive viral disease of maize, Zea mays L., in Argentina. MRCV infection causes abnormal corn development and significantly reduces crop yield. The susceptible phenotype includes stunting, shortened internodes, cut and reduced leaves, deformed tassels with no anthers, reduced roots, underdeveloped ears with poor kernel sets and overall thickening of vascular tissues. The largest known outbreak of MRCV in Argentina to date occurred during the 1996/1997 growing season and affected nearly 300,000 hectares producing approximately $120 MM in yield losses. MRCV disease is vectored by the leafhopper Delphacodes kuscheli. Increased populations of D. kuscheli in 2006 apparently led to a reoccurrence of the viral disease in Argentinean corn plants, which significantly affected the 2007 harvest. Exploratory methods to control the disease using pesticides and other means of insect control have been unsuccessful and development of MCRV tolerant lines through selective breeding is a primary initiative for seed producers.
As Bacillus thuringiensis (Bt) technology becomes more widespread in Brazil and Northern Argentina, the amount of insecticide used on corn crops will most likely decrease. This reduction in insecticide may increase the numbers of leaf hoppers in the environment, thus amplifying MRCV disease pressure. Breeding resistance into corn is the principal and most effective control method to manage yield loss associated with MRCV disease. The development of molecular genetic markers has facilitated mapping and selection of agriculturally important traits in maize, and quantitative trait loci (QTL) for MRCV resistance have been identified. QTL conferring resistance to MRCV have been identified on chromosomes 1 and 8 (DiRenzo et al. 2004; Kreff et al. 2006), chromosome 2 (WO 2009/058335), and chromosomes 4 and 10 (Kreff et al. 2006). Introgression of QTL through the use of molecular markers associated with MRCV will increase the speed and accuracy of moving MRCV resistance into elite corn hybrids, thus improving the level of resistance in subtropical germplasm. Incorporating MRCV resistance into elite corn germplasm may prevent the spread of the viral disease to non-endemic regions.
Despite the fact that information for MRCV resistance QTL is available in the art, few pedigrees can be classified as highly tolerant and there is little evidence of any strong resistance to MRCV in commercially available hybrids. The is still a need for commercially acceptable hybrids that are MRCV resistant and for a method to develop and track resistant maize inbreds and hybrids through marker assisted breeding.
Described within is a method to map MRCV resistance QTL in a DH population using a bi-parental QTL mapping approach. The present invention allows selection of progeny which contain the genomic background of the agronomically desirable parent and the genomic trait of the MRCV resistant donor parent. The present invention also allows tracking of MRCV resistance QTL in order to introgress the MRCV resistance trait into new plants through traditional breeding.